speaker and interconnects, how nice do I need

Buying used is a great Idea. The cheapest speaker cable I have used is 12ga. jacketed in wall cable for ~$0.50/ft..  That and Inexpensive interconnects can be found on Ebay. This would get you by while exploring the market.

A pair of 10" Audioquest Type 4 cables could be had for ~$65.  Check out Ebay also. 

The Canare cable may serve you well. The 4s11can be had for ~$1.50/ft and the 4s8 is less. I bought 20' of the 11s however never put them into service so can't speak to how they sound against the Type 4s. Guess I need to do that. 

Music Direct was selling Audioquest Diamondback interconnects for $75. Can't say if they still are. I bought from them a 0.5m pair sold as demo for $45. Check them out online.

I second JW Audio. I have his interconnects and love them. His speaker cable is ridiculously cheap.
Also consider DNM and anticables.

I concur with the recommendation to start with Canare 4s8 or 4s11 as a baseline for further exploration, if you feel you need to. Buy whatever length you need from some place like https://www.markertek.com/. Don't bother with connectors at first, just twist together the white and red conductors in each cable and connect the bare wire to your amp and speaker terminals. Listen for a good long time and only then begin to explore if you feel it's necessary, or interesting. 

sam-

entry level Transparent will get you started and would jive well w/ your system.  Your listening experience will grow and get better as you advance up the chain of cabling.